U.S. patent application number 10/876012 was filed with the patent office on 2005-03-03 for method and apparatus for alarm volume control using pulse width modulation.
This patent application is currently assigned to BED-CHECK CORPORATION. Invention is credited to Cooper, Craig L., Smith, Toby E..
Application Number | 20050046575 10/876012 |
Document ID | / |
Family ID | 34221412 |
Filed Date | 2005-03-03 |
United States Patent
Application |
20050046575 |
Kind Code |
A1 |
Cooper, Craig L. ; et
al. |
March 3, 2005 |
Method and apparatus for alarm volume control using pulse width
modulation
Abstract
There is provided herein a first preferred arrangement of the
instant invention, wherein an electronic patient monitor utilizes a
computer CPU as an alarm signal generator, which CPU is preferably
directly connected to a power amplifier and/or a speaker without an
intervening (or subsequent) conventional volume control. The alarm
signal is preferably expressed as a series of square waves. The
volume of the alarm signal as heard through the speaker is
controlled by varying the width of the square waves that represent
the alarm signal with the duty cycle of the square waves being
shortened to reduce the output alarm volume and lengthened to
increase it.
Inventors: |
Cooper, Craig L.; (Inola,
OK) ; Smith, Toby E.; (Broken Arrow, OK) |
Correspondence
Address: |
FELLERS SNIDER BLANKENSHIP
BAILEY & TIPPENS
THE KENNEDY BUILDING
321 SOUTH BOSTON SUITE 800
TULSA
OK
74103-3318
US
|
Assignee: |
BED-CHECK CORPORATION
|
Family ID: |
34221412 |
Appl. No.: |
10/876012 |
Filed: |
June 24, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60496501 |
Aug 20, 2003 |
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Current U.S.
Class: |
340/573.1 ;
340/692 |
Current CPC
Class: |
G08B 3/10 20130101; G08B
21/22 20130101 |
Class at
Publication: |
340/573.1 ;
340/692 |
International
Class: |
G08B 023/00 |
Claims
What is claimed is:
1. An electronic patient monitor for use in monitoring a patient,
comprising: (a) a speaker; (b) an amplifier in electronic
communication with said speaker, said amplifier at least for
driving said speaker; (c) a sensor responsive to a status of the
patient; (d) a CPU in electronic communication with said amplifier
and with said sensor, wherein said CPU is at least for monitoring
said status of the patient and sounding an alarm in response
thereto; and, (e) computer storage in electronic communication with
said CPU, said computer storage containing therein at least a
plurality of computer instructions executable by said CPU, said
plurality of computer instructions comprising the steps of: (i)
selecting a volume level, (ii) selecting a duty cycle function
corresponding to said selected volume level, (iii) determining an
alarm type, (iv) obtaining alarm tone data corresponding to said
alarm type, (v) pulse width modulating said alarm tone data with a
series of square waves generated according to said duty cycle
function, thereby producing a series of audio waves at least
approximately representing said selected alarm type when broadcast
through said speaker, and, (vi) transmitting said series of audio
waves to said amplifier for broadcast through said speaker.
2. An electronic patient monitor according to claim 1, wherein said
sensor is a pressure sensitive switch.
3. An electronic patient monitor according to claim 1, wherein said
CPU is chosen from a group consisting of a microprocessor, a
microcontroller, a PLD, a CPLD, an EPLD, a SPLD, a PAL, an FPLA, an
FPLS, a GAL, a PLA, an FPAA, a PSoC, a SoC, a CSoC, and an
ASIC.
4. An electronic patient monitor according to claim 1, wherein said
CPU comprises: (d1) a microprocessor, and, (d2) a sound generation
chip, said sound generation chip being in electronic communication
with said microprocessor and responsive thereto, said sound
generation chip at least for providing in response to said CPU said
alarm tone data according to said determined alarm type.
5. An electronic patient monitor according to claim 1, wherein said
computer storage is selected from a group consisting of ROM, RAM,
flash RAM, PROM, EPROM, magnetic disk, optical disk, and
magneto-optical disk.
6. An electronic patient monitor according to claim 1, wherein step
(e)(iii) comprises the steps of: (1) providing to a user a
plurality of predefined alarm types, and, (2) reading from the user
a selection of one of said plurality of predefined alarm types,
thereby determining an alarm type.
7. An electronic patient monitor according to claim 1, wherein said
duty cycle function is a constant 50% duty cycle.
8. An electronic patient monitor according to claim 1, wherein step
e(vi) comprises the steps of filtering said series of audio waves
and transmitting said series of audio waves to said amplifier for
broadcast through said speaker.
9. An electronic patient monitor according to claim 8, wherein the
step of filtering said series of audio waves comprises the step of
filtering said series of audio waves with a band-pass filter.
10. A method of generated an alarm sound in an electronic patient
monitor at a predetermined volume level, comprising the steps of:
(a) selecting a duty cycle function corresponding to said
predetermined volume level; (b) determining an alarm type; (c)
obtaining alarm tone data corresponding to said alarm type; (d)
pulse width modulating said alarm tone data with a square wave
series formed according to said selected duty cycle function,
thereby creating a series of audio waves at least approximately
representing said selected alarm type when broadcast through a
speaker; and, (e) broadcasting said series of audio waves through
said speaker, thereby generating said alarm sound at approximately
said predetermined volume level.
11. A method of generating an alarm sound in an electronic patient
monitor according to claim 10, wherein the step of selecting a duty
cycle function corresponding to said predetermined alarm volume
level, comprises the step of selecting a duty cycle function
corresponding to said predetermined alarm volume level, wherein
said duty cycle function varies logarithmically with said selected
alarm volume level.
12. An electronic patient monitor according to claim 10, wherein
said duty cycle function is a constant 50% duty cycle.
13. An electronic patient monitor according to claim 10, wherein
said series of audio waves is a series of square waves.
14. An electronic patient monitor for use in monitoring a patient,
comprising: (a) a speaker; (b) a sensor positionable to be
proximate to the patient and responsive to a status of the patient
when so positioned; (c) a CPU in electronic communication with said
sensor and with said speaker, said CPU being at least for (c1)
monitoring said status of the patient via said sensor, and, (c2)
generating at least one alarm in response to a change in said
patient status; (d) computer storage in electronic communication
with said CPU, said computer storage containing therein at least a
plurality of computer instructions readable by said CPU and
executable thereby, said plurality of computer instructions at
least comprising the steps of: (i) using said sensor to determine
that a change in the patient's status has occurred; (ii) selecting
a volume level, (iii) selecting a duty cycle function corresponding
to said selected volume level, (iv) determining an alarm type, (v)
obtaining alarm tone data corresponding to said alarm type, (vi)
generating a series of audio waves according to said duty cycle
function, said alarm type and said tone data, said series of audio
waves at least approximately representing said selected alarm type
when broadcast through said speaker, and, (vi) transmitting said
series of audio wave to said speaker, thereby creating an audible
representation of said determined alarm type.
15. An electronic patient monitor according to claim 14, wherein
said sensor is a pressure sensitive switch.
16. An electronic patient monitor according to claim 14, further
comprising: (e) an amplifier in electronic communication with said
speaker and with said CPU, said amplifier at least for receiving
said audio waves and driving said speaker with said audio
waves.
17. An electronic patient monitor according to claim 14, wherein
said CPU comprises: (c1) a programmable microprocessor, and, (c2) a
sound generation module in electronic communication with said
microprocessor, said sound generation module at least for providing
said alarm tone data of step (v) to said microprocessor.
18. An electronic patient monitor according to claim 14, wherein
said duty cycle function is a constant 50% duty cycle.
19. An electronic patient monitor according to claim 14, wherein
said CPU is a microprocessor and wherein said computer storage is
located within said microprocessor.
20. An electronic patient monitor according to claim 14, wherein
step d(vi) comprises the steps of: (v1) selecting a duty cycle
function corresponding to said selected volume level, said duty
cycle function specifying at least one square wave width and at
least one pulse separation interval, and, (v2) calculating a square
wave representation of at least a portion of said tone data from
said at least one square wave width and said at least one
intra-pulse interval, thereby generating a series of audio waves at
least approximately representing said selected alarm type when
broadcast through said speaker.
21. An electronic patient monitor according to claim 14, wherein
step d(vi) comprises the steps of: (v1) selecting a duty cycle
function corresponding to said selected volume level, said duty
cycle function specifying at least one square wave width and at
least one pulse separation interval, and, (v2) gating said tone
data according to said duty cycle function, thereby generating a
series of audio waves at least approximately representing said
selected alarm type when broadcast through said speaker.
22. An electronic patient monitor for use in monitoring a patient,
comprising: (a) a patient sensor, said patient sensor being
positionable to be proximate to the patient and responsive to a
state of the patient when so positioned; (b) a speaker; (c) sound
circuitry, said sound circuitry at least for creating at least one
audio alarm signal; (d) a control logic circuit in electronic
communication with said speaker, said patient sensor, and said
sound circuitry, said control logic circuit being at least for (d1)
responding to a predetermined change in the state of the patient to
sound an alarm, (d2) receiving said one of said audio signals from
said sound circuitry when said alarm is to be sounded, (d3) pulse
width modulating said received audio signal, thereby setting a
volume level of said audio alarm signal, and (d4) transmitting said
pulse width modulated signal to said speaker.
23. An electronic patient monitor according to claim 22, wherein
said patient sensor is a pressure sensitive switch.
24. An electronic patient monitor according to claim 22, wherein
said control logic circuit is a microprocessor.
Description
RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application Ser. No. 60/496,501 filed on Aug. 20, 2003.
[0002] This invention relates generally to monitoring systems and
more particularly concerns devices and systems used to monitor
seated or lying patients in homes or in medical environments such
as hospitals, assisted care facilities, long term care
institutions, and other care-giving environments, wherein audible
alarms are employed that activate upon a change in the patient's
condition and wherein such alarms are designed to be adjustable in
volume.
BACKGROUND OF THE INVENTION
[0003] It is well documented that the elderly and post-surgical
patients are at a heightened risk of falling. These individuals are
often afflicted by gait and balance disorders, weakness, dizziness,
confusion, visual impairment, and postural hypotension (i.e., a
sudden drop in blood pressure that causes dizziness and fainting),
all of which are recognized as potential contributors to a fall.
Additionally, cognitive and functional impairment, and sedating and
psychoactive medications are also well recognized risk factors.
[0004] A fall places the patient at risk of various injuries
including sprains, fractures, and broken bones--injuries which in
some cases can be severe enough to eventually lead to a fatality.
Of course, those most susceptible to falls are often those in the
poorest general health and least likely to recover quickly from
their injuries. In addition to the obvious physiological
consequences of fall-related injuries, there are also a variety of
adverse economic and legal consequences that include the actual
cost of treating the victim and, in some cases, caretaker liability
issues.
[0005] In the past, it has been commonplace to treat patients that
are prone to falling by limiting their mobility through the use of
restraints, the underlying theory being that if the patient is not
free to move about, he or she will not be as likely to fall.
However, research has shown that restraint-based patient treatment
strategies are often more harmful than beneficial and should
generally be avoided--the emphasis today being on the promotion of
mobility rather than immobility. Among the more successful
mobility-based strategies for fall prevention include interventions
to improve patient strength and functional status, reduction of
environmental hazards, and staff identification and monitoring of
high-risk hospital patients and nursing home residents.
[0006] Of course, direct monitoring of high-risk patients, as
effective as that care strategy might appear to be in theory,
suffers from the obvious practical disadvantage of requiring
additional staff if the monitoring is to be in the form of direct
observation. Thus, the trend in patient monitoring has been toward
the use of electrical devices to signal changes in a patient's
circumstance to a caregiver who might be located either nearby or
remotely at a central monitoring facility, such as a nurse's
station. The obvious advantage of an electronic monitoring
arrangement is that it frees the caregiver to pursue other tasks
away from the patient. Additionally, when the monitoring is done at
a central facility a single person can monitor multiple patients
which can result in decreased staffing requirements and/or more
efficient use of current staff.
[0007] Generally speaking, electronic monitors work by first
sensing an initial status of a patient, and then generating a
signal when that status changes, e.g., he or she has sat up in bed,
left the bed, risen from a chair, etc., any of which situations
could pose a potential cause for concern in the case of an at-risk
patient. Electronic bed and chair monitors typically use a pressure
sensitive switch in combination with a separate electronic monitor
which conventionally contains a microprocessor of some sort. In a
common arrangement, a patient's weight resting on a pressure
sensitive mat (i.e., a "sensing" mat) completes an electrical
circuit, thereby signaling the presence of the patient to the
microprocessor. When the weight is removed from the pressure
sensitive switch, the electrical circuit is interrupted, which fact
is similarly sensed by the microprocessor. The software logic that
drives the monitor is typically programmed to respond to the
now-opened circuit by triggering some sort of alarm--either
electronically (e.g., to the nursing station via a conventional
nurse call system) or audibly (via a built-in siren) or both.
Additionally, many variations of this arrangement are possible and
electronic monitoring devices that track changes in other patient
variables (e.g., wetness/enuresis, patient activity/inactivity,
bed-exit, temperature, position, etc.) are available for some
applications.
[0008] General information relating to mat-type sensors, electronic
monitors and other hardware for use in patient monitoring is
relevant to the instant disclosure and may be found in U.S. Letters
Pat. Nos. 4,179,692, 4,295,133, 4,700,180, 5,600,108, 5,633,627,
5,640,145, and, 5,654,694, U.S. patent application Ser. Nos.
10/701,581 and 10/617,700, U.S. Letters Pat. Nos. 6,111,509,
6,441,742, and U.S. patent application Ser. No. 10/210,817 (the
last three of which concern electronic monitors generally).
Additional information may be found in U.S. Letters Pat. Nos.
4,484,043, 4,565,910, 5,554,835, 5,623,760, 6,417,777, U.S. patent
application Ser. No. 60/488,021, (sensor patents) and U.S. Letters
Pat. No. 5,065,727 (holsters for electronic monitors), the
disclosures of all of which aforementioned patents are all
incorporated herein by reference as if fully set out at this point.
Further, U.S. Letters Pat. No. 6,307,476 (discussing a sensing
device which contains a validation circuit incorporated therein),
U.S. Pat. Ser. Nos. 6,544,200, (for automatically configured
electronic monitor alarm parameters), U.S. Letters Pat. No.
6,696,653 (for a binary switch and a method of its manufacture),
and U.S. patent application Ser. No. 10/125,059 (for a lighted
splash guard) are similarly incorporated herein by reference.
[0009] Additionally, sensors other than mat-type pressure sensing
switches may be used in patient monitoring including, without
limitation, temperature sensors, patient activity sensors, patient
location sensors, bed-exit sensors, toilet seat sensors (see, e.g.,
U.S. Pat. No. 5,945,914), wetness sensors (e.g., U.S. Pat. No.
6,292,102), decubitus ulcer sensors (e.g., U.S. Pat. No.
6,646,556), restraint device sensors (e.g., U.S. patent application
Ser. No. 60/512,042), etc., all of which are incorporated herein by
reference. Thus, in the text that follows the terms "mat" or
"patient sensor" should be interpreted in its broadest sense to
apply to any sort of patient monitoring switch or device, whether
the sensor is pressure sensitive or not.
[0010] Finally, pending U.S. patent application Ser. No.
10/397,126, discusses how white noise can be used in the context of
decubitus ulcer prevention and in other contexts, and U.S. patent
application Ser. No. 60/543,718 teaches the use of medical feedback
systems to reduce the risk of decubitus ulcer formation. Both of
these references are similarly fully incorporated herein by
reference.
[0011] Of particular importance for purposes of the instant
disclosure are those patient monitors that contain audible alarms
that are adjustable in volume. Those of ordinary skill in the art
will recognize that it is desirable in many settings to control the
local alarm volume of the monitor depending on, among other things,
the level of ambient noise, the distance to the caregiver, etc.
However, conventionally the hardware that makes up such volume
controls (e.g., potentiometers, digital potentiometers, etc.) is
expensive and/or prone to failure either by physical damage or
internal corrosion.
[0012] Heretofore, as is well known in the patient monitoring arts,
there has been a need for an invention to address and solve the
above-described problems. Accordingly, it should now be recognized,
as was recognized by the present inventors, that there exists, and
has existed for some time, a very real need for a system for
monitoring patients that contains an adjustable volume alarm with
the features described hereinafter.
[0013] Before proceeding to a description of the present invention,
however, it should be noted and remembered that the description of
the invention which follows, together with the accompanying
drawings, should not be construed as limiting the invention to the
examples (or preferred embodiments) shown and described. This is so
because those skilled in the art to which the invention pertains
will be able to devise other forms of this invention within the
ambit of the appended claims.
SUMMARY OF THE INVENTION
[0014] In accordance with a first aspect of the instant invention,
there is provided a patient sensor and electronic monitor
combination that utilizes pulse width modulation ("PWM") as a means
of controlling the volume of the alarm.
[0015] In a first preferred arrangement, there is provided an
electronic patient monitor that utilizes a CPU as a signal
generator and which is directly connected to a power amplifier
without an intervening (or subsequent) conventional volume control.
The microprocessor preferably creates frequency-varying square
waves (or constant amplitude pulses) according to the sort of alarm
desired by the user, with the duty cycle of the square waves being
shortened to reduce the alarm volume and lengthened to increase
it.
[0016] In another preferred arrangement, there is provided an
electronic patient monitor substantially similar to that described
above, but wherein the CPU directs a separate signal generator to
create the series of pulses. In such a configuration, the separate
signal generator will be programmed to adjust the pulse width so as
to vary the alarm volume.
[0017] In still another preferred arrangement, there is provided an
electronic patient monitor substantially as described above, but
wherein the CPU directly drives the speaker without an intervening
amplifier. As has been explained previously, the CPU will utilize
PWM to control the output volume of the speaker.
[0018] In a further preferred embodiment, there is provided an
electronic patient monitor substantially as described above, but
wherein the square wave/pulse series takes the form of series of
gating pulses that restrict the amount of audio information that
reaches the amplifier and/or speaker.
[0019] The foregoing has outlined in broad terms the more important
features of the invention disclosed herein so that the detailed
description that follows may be more clearly understood, and so
that the contribution of the instant inventor to the art may be
better appreciated. The instant invention is not to be limited in
its application to the details of the construction and to the
arrangements of the components set forth in the following
description or illustrated in the drawings. Rather, the invention
is capable of other embodiments and of being practiced and carried
out in various other ways not specifically enumerated herein.
Further, the disclosure that follows is intended to apply to all
alternatives, modifications and equivalents as may be included
within the spirit and scope of the invention as defined by the
appended claims. Finally, it should be understood that the
phraseology and terminology employed herein are for the purpose of
description and should not be regarded as limiting, unless the
specification specifically so limits the invention.
[0020] While the instant invention will be described in connection
with one or more preferred embodiments, it will be understood that
it is not intended to limit the invention to those embodiments. On
the contrary, it is intended to cover all alternatives,
modifications and equivalents as may be included within the spirit
and scope of the invention as defined by the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] Other objects and advantages of the invention will become
apparent upon reading the following detailed description and upon
reference to the drawings in which:
[0022] FIG. 1 illustrates the general environment of the instant
invention, wherein an electronic patient monitor is connected to a
bed mat.
[0023] FIG. 2 illustrates the general environment of the instant
invention, wherein an electronic patient monitor is connected to a
chair mat.
[0024] FIG. 3 contains an illustration of the main features of a
preferred embodiment of the instant electronic patient monitor.
[0025] FIG. 4 is a schematic illustration of a preferred embodiment
of the instant invention.
[0026] FIG. 5 illustrates in a general way how the signal pulse
width is related to the output volume.
[0027] FIG. 6 is a circuit diagram of a preferred embodiment of the
instant patient monitor.
[0028] FIG. 7 contains a preferred operating logic of the inventive
method taught herein.
[0029] FIG. 8 illustrates preferred embodiment of the instant
invention, wherein a separate sound module is utilized that is
external to the CPU.
[0030] FIG. 9 contains an illustration of how the instant PWM
method could be used to adjust the volume of an arbitrary sound
source.
[0031] FIG. 10 illustrates some embodiments wherein the CPU is
directly connected to the loudspeaker and an amplifier is not
used.
[0032] FIG. 11 contains an illustration of a preferred embodiment
of the instant invention which utilizes an analog switch to control
the volume of an arbitrary sound source.
[0033] FIG. 12 contains a schematic illustration of another
preferred embodiment, wherein a differential amplifier is used to
create an alarm signal that has reduced DC bias.
[0034] FIGS. 13A, 13B, and 13C illustrate how two time-shifted
square waves can be combined to yield a signal with a minimal DC
component.
[0035] FIG. 14 contains a preferred arrangement wherein a
flip-flop/logic circuit is used to produce a pair of output signals
suitable for input to a differential amplifier to produce a reduced
DC component signal.
[0036] FIG. 15 illustrates a method by which PWM may be utilized in
connection with an arbitrary waveform to control the volume of a
patient monitor.
[0037] FIG. 16 contains an illustration of another preferred
embodiment wherein a square wave pulse train is used to gate an
arbitrary signal.
[0038] FIG. 17 illustrates a square wave time series suitable for
varying the volume in a speaker to match an arbitrary waveform.
[0039] FIG. 18 contains a preferred embodiment of the instant
invention which is implemented in discrete logic.
DETAILED DESCRIPTION OF THE INVENTION
[0040] According to a preferred aspect of the instant invention,
there is provided an electronic patient monitor for use with at
least one patient sensor, wherein the volume of the monitor's alarm
sounds is controlled by using PWM rather than via a conventional
hardware volume control.
General Environment of the Invention
[0041] Generally speaking, electronic patient monitors of the sort
discussed herein work by first sensing an initial status of a
patient, and then generating a signal when that status changes
(e.g., if the patient changes position from laying or sitting to
standing, if the sensor changes from dry to wet, if a temperature
spike occurs, if the patient rolls, etc.) or if the status fails to
change (e.g., if the patient has not moved within some
predetermined time period). Turning now to FIG. 1 wherein the
general environment of one preferred embodiment of the instant
invention is illustrated, in a typical arrangement a pressure
sensitive mat 100 sensor is placed on a hospital bed 20 where it
will lie beneath a weight-bearing portion of the reclining
patient's body, usually the buttocks and/or shoulders. Generally
speaking, the mat 100/electronic monitor 50 combination works as
follows. When a patient is placed atop the mat 100, the patient's
weight compresses it, thereby closing an internal electrical
circuit. This circuit closure is sensed by the attached electronic
patient monitor 50 and, depending on its design, this closure may
signal the monitor 50 to begin monitoring the patient via the mat
100. Additionally, in some embodiments, the monitoring phase is
initiated by a manually engaged switch. Thereafter, when the
patient attempts to leave the bed, weight is removed from the
sensing mat 100, thereby breaking the electrical circuit, which
interruption is sensed by the attached electronic patient monitor
50. The patient monitor 50, which conventionally contains a
microprocessor therein, then signals the caregiver per its
pre-programmed instructions. In some cases, the signal will amount
to an audible alarm or siren that is emitted from the unit 50. In
other cases, an electronic signal could be sent to a remote
nurses/caregivers station via electronic communications line 60.
Note that additional electronic connections not pictured in this
figure might include a monitor power cord to provide a source of AC
power although, as generally pictured in this figure, the monitor
50 can certainly be configured to be either battery or AC
powered.
[0042] In another common arrangement, and as is illustrated in FIG.
2, a pressure sensitive chair sensor 200 might be placed in the
seat of a wheel chair or the like for purposes of monitoring a
patient seated therein. As has been described previously, a typical
configuration utilizes a pressure sensitive mat 200 that is
connected to an electronic chair monitor 250 that is suspended from
the chair 30. Because it is anticipated that the patient so
monitored might choose to be at least somewhat mobile, the monitor
250 will usually be battery powered and will signal a chair-exit
event via an internal speaker, rather than a hardwired nurse-call.
Of course, those of ordinary skill in the art will understand that
in some instances the monitor 250 will be configured to communicate
wirelessly with the nurses' station through IR, RF, ultrasonic or
some other communications technology.
PREFERRED EMBODIMENTS
[0043] In accordance with a first aspect of the instant invention
and as is generally shown in FIG. 3, there is provided a patient
monitor 300 which is designed to operate without conventional
volume control circuitry but which instead utilizes pulse width
modulation ("PWM") to adjust the output volume level of the speaker
310.
[0044] Preferably the monitor will utilize connector 320 to
interface with the patient sensor 100. In some preferred
configurations the interface 320 is compatible with an RJ-11-type
jack. Preferably the sensor will be a mat-type pressure sensitive
sensor, however it should be clear that the type of sensor that is
employed is immaterial to the operation of the instant invention.
That is, no matter what form the attached sensor might take (e.g.,
presence/absence, position, wetness, temperature, pressure,
movement, etc.) the volume adjusting portion of the instant patient
monitor would operate in exactly the same fashion. As is typical in
individual patient monitors, each unit is equipped with a speaker
310 through which an audio alarm may be issued.
[0045] Turning now to FIG. 4 wherein a schematic diagram of a
preferred embodiment is presented, the CPU 420 will have access to
some amount of storage 410 which could be used to store its
controlling program. Preferably, the storage 410 will take the form
of non-volatile memory (e.g., ROM, flash RAM, etc.), which might be
either internal or external to the CPU 420. That being said, those
of ordinary skill in the art will recognize that conventional
computer memory is only one of many possible storage sources that
might be used and alternatives such as magnetic disk, remote hard
disk (e.g., booting over a network), optical disk, magneto-optical
disk, etc. Thus, for purposes of the instant invention, when the
words "memory" or "storage" are used, those terms should be
interpreted in the broadest sense to include any sort of electronic
data storage that is accessible by the CPU 420, whether that
storage is internal to the monitor 300 or external to it.
[0046] In electronic communication with CPU 420, and preferably
external to it, is a power amplifier 440, the purpose of which is
to amplify the signal that is sourced in CPU 420. The speaker 310
then preferably broadcasts the amplified signal in the vicinity of
the monitor 300. However, those of ordinary skill in the art will
recognize that the speaker 310 need not be made integral to the
monitor 300, but could instead be located remotely from the CPU 420
(e.g., located in the hall outside of the patient's room, located
at the nurses' station, etc.). The speaker 310 will preferably be a
cone-type loudspeaker but, clearly, it could be any sort of device
that can reproduce sound and that can be driven from a power
amplifier 440. Additionally, the speaker 310 could certainly be a
piezoelectric or similar device and, especially preferably, it will
be a piezoelectric device that is driven directly from the
microprocessor without an intervening amplifier (see, e.g., FIG. 1
0A where speaker 310 is a piezoelectric device).
[0047] In a preferred arrangement, a volume control switch 330 is
provided on the exterior of the case so that the user can select
from among a plurality of different volume levels. The CPU 420 is
preferably placed in electronic communication with the switch 330
so that the user's volume choice can be read and acted upon. In a
typical arrangement, the user will be provided with eight different
volume levels (zero to 7, say) which are cycled through by
repeatedly pressing switch 330. Often there will also be provided a
visual indication of the selected alarm volume (e.g., an LED or
similar display device) that displays the currently selected
numeric volume. Preferably, the CPU 420 will control the reading
and display of the selected volume information according to methods
well known to those of ordinary skill in the art.
[0048] FIG. 5 illustrates a fundamental aspect of the instant
invention. As is generally illustrated in that figure, the instant
inventors have determined that when the pulse width of a constant
frequency square-wave signal is varied, other things remaining
equal, the output volume emitting from the speaker varies
commensurately. Consider, for purposes of illustration, the CPU 420
generated input wave trains 510 and 530 in FIG. 5. Note that both
have the same period (T) and the same amplitude, however each has a
different pulse width W.sub.1 and W.sub.2, respectively. However,
note that the amplitude of the output sounds 520 and 540 resulting
from such input signals, while having the same output frequency,
differ in amplitudes, i.e., A.sub.1 and A.sub.2, respectively. This
suggests that, rather than utilizing conventional volume control
hardware, the microprocessor itself can create signals which vary
the output volume of the alarm
[0049] In brief, the duty cycle of the input signal that is
transmitted to the amplifier 440 (e.g., signals 510/530) is
directly correlated with the speaker 310 output volume. Thus, by
changing the duty cycle of the signal that is generated by the CPU
420, the alarm volume can be changed. Those of ordinary skill in
the art will recognize that the exact volume that is produced by a
particular duty cycle choice is one that can readily be determined
for any particular hardware configuration and duty cycle. A
preferred method of determining at least a rough correspondence is
through the use of trial and error. For example, if a number of
different duty cycles are selected and broadcast through the
speaker 310, the resulting volumes can be measured and recorded,
thereby providing a profile of the impulse-response of that
particular hardware combination. Additionally, the instant
inventors would note that, generally speaking, if uniformly-spaced
speaker volumes are desired, the corresponding duty cycles choices
are likely to be logarithmically distributed between zero and 50%
duty cycle.
[0050] A typical hardware configuration for the instant invention
is set out in FIG. 6. In a preferred embodiment, an output port of
CPU 420 will be routed to amplifier 620. Preferably, the output of
amplifier 620 will be filtered by a low pass filter, such as RC
filter 610. One purpose of this audio filter is to attenuate the
resultant harmonics that are caused by the use of square waves. In
the preferred embodiment, the resistor and capacitor are chosen to
be 12K ohms and 0.15 microfarads, respectively, which
conventionally results in an upper frequency cutoff at 884 Hertz
(i.e., 1/2.pi.RC), with a roll off of 3 db per octave for
frequencies above that. Needless to say, the selection of the
particular pass band for this filter and its roll off rate are
design choices that are well within the ability of one of ordinary
skill in the art to determine.
[0051] Note that in another preferred arrangement and as is
generally indicated in FIG. 13C, the generated square waves will
alternate in sign, thereby eliminating or reducing the DC component
of the signal. As those of ordinary skill in the art will
recognize, if a series of positive square waves (i.e., the wave
values alternate between +1 and 0) is transmitted to a speaker a DC
bias will be introduced, thereby reducing the efficiency of the
system. As a consequence, and according to another preferred
embodiment, there is provided a patient monitor substantially as
described above, but wherein the square waves alternate in sign so
as eliminate or reduce the DC bias in the alarm signal. FIGS. 13A
and 13B indicate how the signal of FIG. 13C can readily be
constructed by combining one square wave series with a second that
is a delayed and inverted version of the first. FIG. 14 illustrates
a preferred hardware arrangement for creating the signal of FIG.
13C.
[0052] As is generally indicated in FIG. 12, in still another
preferred embodiment a differential amplifier 1210 is placed in
electronic communication with a microprocessor 1220. In this
embodiment, the microprocessor 1220 will preferably have two
independent PWM generators therein, each of which preferably
provides an output through a different port. Preferably, the signal
transmitted through line 1240 will be a square wave of the same
frequency as that transmitted through line 1230, but shifted by
one-half of the period. This is perhaps more clearly illustrated by
comparison of FIGS. 13A and 13B, wherein the second series is
shifted with respect to the first. The inputs 13A and 13B will
result at least approximately in the signal of FIG. 13C being sent
to the speaker 310. Note that, as discussed previously, the alarm
signal of FIG. 13C is symmetric about zero and, as a consequence,
its DC component is at least theoretically equal to zero.
[0053] Other preferred configurations are set out in FIG. 10A,
wherein the power amplifier has been eliminated and instead the
speaker 310 is driven directly from two ports of the microprocessor
420. In the preferred arrangement, two ports (e.g., ports PA0 and
PA1) will be utilized and placed in electronic communication with
the speaker terminals as is generally illustrated in FIG. 10.
Preferably, of course, the microprocessor will be protected by one
or more resistors as is generally illustrated in this figure.
Finally, in such an arrangement it is preferred that the electrical
polarity of the two chosen ports be opposite, i.e.,
PA1=({overscore (PA0)}).
[0054] Those of ordinary skill in the art will readily recognize
how an inverted square wave series in one port can simultaneously
be generated in the other port. Of course, in general it would be
impractical to drive large speakers at substantial volume levels
with the power available from a microprocessor. However, small
speakers such as those preferably utilized in connection with the
instant invention can certainly be driven at some volume levels by
the microprocessor 420 alone. FIG. 10B illustrates a similar
arrangement, but wherein two speakers 310 are connected in series.
Those of ordinary skill in the art will recognize that additional
speakers beyond two could similarly be connected. Finally, FIG. 10C
illustrates a preferred embodiment wherein a lower pass filter is
placed between CPU 420 and the speaker 310.
[0055] According to still another embodiment, and as is generally
illustrated in FIG. 11, there is provided an apparatus
substantially as described above, but wherein an analog switch,
electronic optical coupler, or similar electronic gating device, is
used to gate an arbitrary input signal using PWM, thereby
controlling its volume without the use of a separate volume
control.
[0056] As is set out in FIG. 11, in a preferred arrangement a
separate sound circuit 810 is used to generate an audio signal. Of
course, that is not essential and those of ordinary skill in the
art will recognize that it is certainly possible to use the CPU 420
for this purpose. The sound circuit 810 might be of any type
including, for example, a dedicated digital signal processing
("DSP") chip, but one preferred arrangement utilizes a voice chip
or similar circuitry to generate a spoken alarm. Such a voice chip
might allow the user to record his or her own vocal alarm, but that
is not required.
[0057] As is generally illustrated in FIG. 11, it is preferable
that CPU 420 be in electronic communication with sound circuit 810
so that the microprocessor can activate/deactivate the generation
of alarm sounds according to its programming. CPU 420 preferably
generates a series of square waves, the pulse width of which is
selected depending on the desired output volume. However, rather
than routing the square wave series directly to the amplifier
440/speaker 310 as was taught previously, the square wave signal in
this embodiment is used to gate the alarm that originates in sound
circuit 810. That is, it is well known to those of ordinary skill
in the art that an analog or digital switch 1110 is designed such
that when the line between it and CPU 420 is "high" the signal from
sound source 810 will be passed through unchanged. However, when
the CPU 420 line is low, no information is passed on to amplifier
440. In the preferred arrangement, the square-wave series will be
generated at a very high frequency, e.g. 100 kHz or so. Note
further that, in contrast to the case where the square waves are
directly submitted to the amplifier, in this case maximum volume is
not at the 50% duty cycle mark, but rather at the point where the
CPU line is constantly held "high", i.e., when the original signal
is allowed to pass through unchanged. As has been described
previously, when the generated pulse widths are wider,
correspondingly more power will be sent through to amplifier 440
and, hence, a greater output sound volume will result. Thus, the
output volume through speaker 310 will be modified in proportion to
the width of the pulses generated by the CPU 420.
[0058] In practice, the instant invention will preferably operate
according to the method generally set out in FIG. 7. As a first
preferred step in the instant PWM volume control method 700, the
CPU 420 will read the user-selected volume level (step 705). The
selected volume will then preferably be matched up with a
corresponding duty cycle (step 710), preferably by looking up the
corresponding value in a table which has previously been calculated
and placed in storage 410 or elsewhere so that it may be accessed
by the CPU 420. A preferred method of building a table that relates
speaker volume and duty cycle has been discussed previously.
[0059] As a next preferred step 715, the CPU 420 will select an
alarm type. That is, in a typical arrangement the user will be
offered a selection of different alarm sounds such as sirens,
warbles, swoops, songs (e.g., "Mary had a little lamb"), etc. Note
that, for purposes of the instant disclosure, even if there is but
a single alarm sound type provided it will be understood that it is
"selected" at this step.
[0060] Once the alarm has been selected, the tone data associated
with it will be read (step 720), preferably by the CPU 420. In the
preferred embodiment, the tones that make up such alarms are kept
in the form of a table that contains the frequency and duration of
each tone such that by sequentially playing each tone for the
indicated duration the desired alarm sound will be heard through
the speaker 310. Those of ordinary skill in the art will recognize
that this sort of arrangement is routinely utilized in this
industry to store relatively simple alarm sounds. Alternatively,
the alarm might consist of more complex digitized audio information
(e.g., the alarm could be the prerecorded spoken message "Please
get back into bed"). Note that, for purposes of the instant
disclosure, when the alarm sound is an arbitrary digitized sound
the "tone data" for such a sound is the individual digital sound
samples together with any other parameter(s) that might be required
to reproduce the sound (e.g., the sample rate). Further, in the
case where the alarm sound is dynamically (e.g., algorithmically or
mathematically) generated, whether within a microprocessor or
within a DSP microcontroller, the tone data refers to the
parameters that define such a sound. Examples of such
algorithmically generated alarm sounds would include white
noise-based alarms, alarms that consist of collections of simple
sine or cosine waves, square waves, triangular waves, etc. The
methods by which these and many other such waveforms might be
generated are well known to those of ordinary skill in the art.
[0061] Note that, and as is illustrated in FIG. 8, it is certainly
possible that the CPU 420 might be used in conjunction with a
separate sound generating module 810, so that the CPU 420 would
issue commands to the sound module 810 which, in turn, actually
would be responsible for playing the selected alarm sound through
the speaker 310 using PWM. That being said, for purposes of the
instant disclosure, when the term "CPU" is used, that term should
be understood and broadly construed to include the microprocessor
as well as any support or other chips that are used in concert with
the CPU to produce pulse width-modulated signals according to the
methods of the instant invention.
[0062] Next, the preferred method enters a loop (steps 725 through
740) wherein the tones that define the alarm are successively
selected, generated as a series of square waves, and transmitted to
the amplifier. Step 725 selects the first or, after the loop has
been entered, the next tone in the alarm definition. Preferably,
the data for each tone will consist of a frequency and a tone
duration. Clearly, this sort of data will be suitable to describe
host of simple alarm patterns. However, in the event that the alarm
is more sonically complex (e.g., a recorded or synthesized voice or
an orchestral musical work), the data that is read will preferably
be successive samples of a digitized audio that has been collected
at a predetermined sample rate. The handling of more sonically
complex alarms will be separately discussed below.
[0063] As a next preferred step 730, a series of constant frequency
square waves will be generated at the frequency specified by the
tone data. Thus, if the tone frequency is 440 Hz, 440 square waves
will be generated per second. Note that, although such a series of
square waves might readily be manually generated in software, many
microprocessors contain the ability to generate square waves as a
built-in software or hardware function.
[0064] The width of each square wave will be determined from the
user's selected volume level in concert with the frequency of the
pulses. That is, given the specified frequency the width (time
duration) of each square wave can readily be determined at the
maximum duty cycle of 50%. However, if the alarm volume is less
than maximum, it is preferred that the width of each square wave be
scaled logarithmically. Alternatively, the alarm volume might be
scaled linearly, although approach typically does not produce
equally spaced perceived volume changes. As a simple example,
suppose that the specified frequency is 440 Hz, this would mean
that at maximum volume each square wave would have a on-time of
about 0.00114 seconds (0.00227/2.0), followed by the same amount of
"off" time when the signal is "zero". Note, however, that would be
the preferred pulse duration at full volume. At, for example,
volume "3" (of 8 possible volume levels), the duration of the duty
cycle could be scaled linearly from the maximum volume and
calculated to be (3/8)*(0.00227 seconds) which equals approximately
0.00085 seconds. That being said, those of ordinary skill in the
art will recognize that equally spaced power-level changes will not
be perceived as equally spaced volume changes by the listener.
Thus, it is preferred instead that logarithmic spacing of the
volume levels be utilized to scale the square waves according to
methods well known to those of ordinary skill in the art.
[0065] As a next preferred step, the square waves will be
sequentially transmitted to the amplifier 440. In the preferred
arrangement, the microprocessor will alternately set a
predetermined port to high and low (i.e., "1" and "0") according to
the timing calculated above. The amplifier 440 receives the
sequence of square waves and then amplifies that signal for
broadcast by the speaker 310.
[0066] Next, an inquiry is preferably made as to whether or not the
alarm is to be terminated (step 735). If the alarm has been
properly terminated, the monitor would be expected to stop its
broadcast (step 745).
[0067] On the other hand, if the alarm has not been terminated, an
inquiry will preferably be made as to whether there is another tone
available in the tone definition for this alarm (step 740). If so,
the preferred algorithm will proceed to read that tone and transmit
it for the time period indicated. If there are no further tones
(e.g., if the end of the song has been reached), the instant method
preferably resets the tone counter (step 750) to the first tone in
the alarm (e.g., the first note of the song "Mary had a little
lamb") and steps 725 through 740 will be repeated as has been
previously described.
[0068] Turning now to a more complex scenario, e.g., an alarm sound
that is a sampled or synthesized multi-frequency waveform, while
there are many possible methods of using PWM to scale such a
signal, a first preferred method is generally illustrated in FIG.
9. As is indicated in that figure, it will be assumed that the
input signal 910 has been sampled and is represented by sample
points 940 which have been taking at a sampling interval AT. In
such a case, a square wave sequence 920 will be created at a
shorter sampling interval At so that there will be N square waves
per original sample, with the additional samples being generally
indicated by points 950. Preferably, .DELTA.t will be some fraction
of .DELTA.T (e.g., one-tenth) so that N will generally be defined
to be equal to .DELTA.T/.DELTA.t (or, 10 if .DELTA.t is one tenth
of .DELTA.T). Each original sample 910 is thus represented by N
square waves. In FIG. 9, for purposes of illustration only N has
been chosen to be equal to three.
[0069] Given the previous arrangement, a series of preferably
equally spaced (.DELTA.t) square waves are generated, wherein the
width of each square wave is determined by the amplitude of one or
more of the original samples 940. That is, in FIG. 9 note that the
pulse width of the first three pulses 920 is greater than that of
the next three, etc., which mirrors the changes in amplitude of the
original signal. Because the amplifier at least approximately acts
as an integrator, the net result of amplifying and broadcasting
such a signal will be that each of the original samples 910 will be
reproduced via the speaker 310 at an amplitude that is proportional
to the original volume, scaled, of course, by the selected overall
volume level as reflected in the pulse widths. In this manner, any
arbitrary sampled waveform may be utilized as an alarm and have its
volume varied without the use of separate volume control
circuitry.
[0070] Additionally, and preferably, rather than choosing the
square wave series 920 to be of uniform pulse width, the input
signal 910 will preferably be interpolated at points 950 (i.e., at
sampling interval .DELTA.t) and each of the corresponding square
waves in the series 920 scaled according to an interpolated value.
This means that the pulse width of the square wave series 920 is
continuously varied according to the instantaneous amplitude of the
input signal 910. Note that, although linear interpolation was used
in this case, any other form of interpolation would work as well
including, without limitation, general polynomial interpolation,
spline interpolation, etc. Those of ordinary skill in the art will
recognize that this is just one of many ways that the volume of a
sampled waveform can be controlled according to the methods taught
herein.
[0071] It should be noted and remembered that, although the instant
invention preferably operates with square waves, in reality an
arbitrary waveform can be utilized to control the speaker volume as
is taught herein. That is, and in still another preferred
embodiment, as is generally illustrated in FIG. 15, given an
arbitrary waveform as input (left side of FIG. 15), the
time-on/duty cycle of that waveform may be readily modified by
gating, with the width of the gate used being proportional to the
desired output volume. As can be seen in FIG. 15, the right-hand
series is the same as the left-hand series, except that in the
right-hand series the trailing half of each wavelet has been
truncated (e.g., by gating). Note that the output volume of the
speaker will be minimum when very narrow gates are used and at
maximum when the gates approach a 100% duty cycle. This concept is
further illustrated in FIGS. 16A and 16B. In this figure, input
waveform 1610 is gated via square wave series 1620 and 1640, the
second of which contains narrower gating. As can be seen, the
consequences of such gating in both cases (i.e., series 1630 and
series 1650) is a time series that closely resembles the input
1610, except, of course, that in the second gating (FIG. 16B) the
amount of information/energy that is passed by the gate in series
1650 is less than is present in series 1630. Finally, curve 1635 is
a schematic representation of the consequence of broadcasting
series 1630 through a speaker. This curve should be compared with
the corresponding/lower volume curve 1655 which represents the
output signal that might be expected by broadcasting series
1650.
[0072] According to still another preferred embodiment, there is
illustrated in FIG. 17 a variation wherein the pulse train 1720
representation of input signal 1710 is comprised of a series of
equal width square waves, but wherein their spacing is related to
the amplitude of the input source 1710. That is, in this
arrangement constant-width square waves are utilized to represent
the input signal, with the square waves coming more frequently in
areas of higher amplitude. When the pulse train is broadcast
through an associated speaker or amplifier/speaker combination, the
energy input per unit interval of time will vary proportionally
with the frequency with which the pulses arrive, thereby creating a
representation of the input signal Those of ordinary skill in the
art will recognize that the inverse of the pulse train 1720 more
closely resembles a conventional PWM time series than does the
original series.
[0073] Finally, and as is generally indicated in FIG. 18, there is
provided another preferred embodiment of the instant invention 1800
that is implemented without using a CPU or similar device. Those of
ordinary skill in the art will recognize that a discrete logic
square wave generator may readily be constructed that would be
suitable to replace the CPU for purposes varying the alarm volume.
In FIG. 18, one of the functions of control logic circuitry 1810 is
to provide source of square waves that will be used to pulse-width
modulate the output from sound circuitry 810 in preparation for
transmitting the resulting signal to power amplifier 440 where it
will be subsequently broadcast via speaker 310. By way of example
only, the square-wave generation portion of control logic circuitry
1810 might be construed by using a ring counter to drive a D to A
converter (e.g., an R-2R ladder) that feeds the trigger input of a
retriggerable one-shot multi vibrator in free run mode. It should
be noted that the sound circuitry 810 could be a component within
the control logic circuitry 1810 or it might exist as a separate
component. In one preferred embodiment, the sound circuitry 810
could be as simple as an astable multi-vibrator. In view of the
foregoing, it should be understood that, although the preferred
embodiment utilizes a CPU to generate square waves, that component
is not strictly required and that the CPU might be replaced with a
combination of discrete logic components.
Conclusions
[0074] Note that if a microprocessor is utilized as a component of
the monitor 300, the only requirement that such a component must
satisfy is that it must minimally be an active device, i.e., one
that is programmable in some sense, that it is capable of
recognizing signals from a bed mat or similar patient sensing
device, and that it is capable of initiating the sounding of one or
more alarm sounds in response thereto. Of course, these sorts of
modest requirements may be satisfied by any number of programmable
logic devices ("PLD") including, without limitation, gate arrays,
FPGA's (i.e., field programmable gate arrays), CPLD's (i.e.,
complex PLD's), EPLD's (i.e., erasable PLD's), SPLD's (i.e., simple
PLD's), PAL's (programmable array logic), FPLA's (i.e., field
programmable logic array), FPLS (i.e., fuse programmable logic
sequencers), GAL (i.e., generic array logic), PLA (i.e.,
programmable logic array), FPAA (i.e., field programmable analog
array), PsoC (i.e., programmable system-on-chip), SoC (i.e.,
system-on-chip), CsoC (i.e., configurable system-on-chip), ASIC
(i.e., application specific integrated chip), etc., as those
acronyms and their associated devices are known and used in the
art. Further, those of ordinary skill in the art will recognize
that many of these sorts of devices contain microprocessors
integral thereto. Thus, for purposes of the instant disclosure the
terms "processor," "microprocessor" and "CPU" (i.e., central
processing unit) should be interpreted to take the broadest
possible meaning herein, and such meaning is intended to include
any PLD or other programmable device of the general sort described
above.
[0075] Additionally, in those embodiments taught herein that
utilize a clock or timer or similar timing circuitry, those of
ordinary skill in the art will understand that such functionality
might be provided through the use of a separate dedicate clock
circuit or implemented in software within the microprocessor. Thus,
when "clock" or "time circuit" is used herein, it should be used in
its broadest sense to include both software and hardware timer
implementations.
[0076] Note further that a preferred electronic monitor of the
instant invention utilizes a microprocessor with programming
instructions stored therein for execution thereby, which
programming instructions define the monitor's response to the
patient and environmental sensors. Although ROM is the preferred
apparatus for storing such instructions, static or dynamic RAM,
flash RAM, EPROM, PROM, EEPROM, or any similar volatile or
nonvolatile computer memory could be used. Further, it is not
absolutely essential that the software be permanently resident
within the monitor, although that is certainly preferred. It is
possible that the operating software could be stored, by way of
example, on a floppy disk, a magnetic disk, a magnetic tape, a
magneto-optical disk, an optical disk, a CD-ROM, flash RAM card, a
ROM card, a DVD disk, or loaded into the monitor over a network as
needed. Additionally, those of ordinary skill in the art will
recognize that the memory might be either internal to the
microprocessor, or external to it, or some combination. Thus,
"program memory" as that term is used herein should be interpreted
in its broadest sense to include the variations listed above, as
well as other variations that are well known to those of ordinary
skill in the art.
[0077] Additionally, although the term "duty cycle" has
occasionally been used herein in a manner that might suggest that a
single-valued duty cycle (e.g., 50%) is intended by the inventors,
that interpretation would unnecessarily limit the broader meaning
taught by this invention. That is, and as has been discussed
previously the "duty cycle" in many cases might be chosen to be a
continuously varying pulse width rather than any single constant
value. More generally, the "duty cycle function" could specify any
arbitrary combination of time-varying pulse width and pulse
separation interval, so long as the pulse train was composed of
constant amplitude rectangular pulses. Thus, the phrases "duty
cycle" and "duty cycle function" should be interrupted herein in
the broadest possible sense to include single valued/constant duty
cycles as well as arbitrarily complex time-varying duty cycle
changes.
[0078] Further, it should be noted that the term "alarm" as used
here should not be limited to traditional alarms and alarm sounds
(e.g., sirens, warbles, etc.) but instead should be broadly
construed to include any audible signal that might be broadcast by
an electronic patient monitor, e.g., soothing/calming sounds (e.g.,
white or colored noise that is designed to mask ambient sounds),
musical works, digitized speech, feedback beeps that are sounded in
connection with button presses, etc.
[0079] Still further, it should be noted that when the term "square
wave" is used herein, that term should not be limited to cases
where the "on" time and the "off" time (i.e., the pulse separation
interval) are equal but instead should be broadly construed to
include any sort of constant amplitude rectangular wave or pulse
that alternates between two values (e.g., between +1 V and 0 V) or
between three values (e.g., between +0.5 V, 0.0 V, and -0.5 V),
even if the duration of each pulse and/or the time-separation
between successive pulses is not a constant value.
[0080] Additionally, it should be noted and remembered that
although patient exit monitors are a preferred environment for
application of the instant invention, the teachings disclosed
herein have much further application. In brief, the instant
invention is most suitable for use in electronic patient monitoring
applications, patient feedback control systems, and similar
applications.
[0081] Finally, it should be noted that the term "nurse call" as
that term has been used herein should be interpreted to mean, not
only traditional wire-based nurse call units, but more also any
system for notifying a remote caregiver of the state of a patient,
whether that system is wire-based (e.g., fiber optics, LAN) or
wireless (e.g., R.F., ultrasonic, IR link, etc.). Additionally, it
should be clear to those of ordinary skill in the art that it may
or may not be a "nurse" that monitors a patient remotely and, as
such, nurse should be broadly interpreted to include any sort of
caregiver, including, for example, untrained family members and
friends that might be signaled by such a system.
[0082] Thus, it is apparent that there has been provided, in
accordance with the invention, a patient sensor and method of
operation of the sensor that fully satisfies the objects, aims and
advantages set forth above. While the invention has been described
in conjunction with specific embodiments thereof, it is evident
that many alternatives, modifications and variations will be
apparent to those skilled in the art and in light of the foregoing
description. Accordingly, it is intended to embrace all such
alternatives, modifications and variations as fall within the
spirit of the appended claims.
* * * * *